Many trains ran behind schedule because of the poor visibility while road traffic moved at a snail's pace.
The dense fog will continue for the next five to six days due to "unstable weather conditions" and high humidity level, a Met official said.
He said western disturbance is likely to pass through the city on January 23 which may result in rain and further deterioration in the weather condition. The city is likely to witness dense fog during the Republic Day celebration on January 26.
The minimum temperature was recorded at 7.2 degrees Celsius today, against yesterday's 6.6 deg C while maximum temperature in the last 24 hours was recorded at 18.6 deg C -- two notches below normal.
An airport official said 27 domestic and international flights were diverted, 18 cancelled and around 20 rescheduled since last night because of the poor runway visibility.
Air connectivity between New Delhi and Himachal Pradesh snapped again on Thursday.
"Flights from Delhi to Shimla and to Bhuntar (near Kullu) were snapped today (Thursday) due to dense fog in Delhi. The flights are likely to resume tomorrow (Friday)," an official at the airport said.
The Shimla airport remained shut for five days from Jan 1 due to foggy conditions in Delhi.
Kingfisher is the only airline that operates flights in the hill state.
Yesterday, over 170 flights were either delayed, rescheduled or cancelled after dense fog enveloped the airport for over 11 hours.
Deccan Herald is on WhatsApp Channels| Join now for Breaking News & Editor's Picks